Method of and apparatus for superheating oil in vapor phase



Oct.` 3, 1939.

F. H. PRAEGER ET AL METHOD OF AND APPARATUS FOR SUPERHEATING OIL INVAPOR PHASE Filed Julle 9, 1938 2 Sheets-Sheet l Haz/ff 2 IN VENT OR.

JMMML ATTORNEY.

Oct. 3, 1939. F, Hl PRAEGER ET AL METHOD OF AND APPARATUS FORSUPERHEATING OIL IN VAPOR PHASE Filed June 9, 1938 2 Sheets-Sheet 2Patented Oct. 3, 1939 UNITED STATES PATENT OFFICE METHOD OF ANDlAPPARATUS FOR SUPER- HEATING OIL IN VAPOR PHASE ration of DelawareApplication June 9, 1938, Serial No. 212,850

8 Claims.

Our invention relates to methods of and apparatus for superheating oilin Vapor phase, and has for an object the provision of a simple reliableand inexpensive means of superheating oil vapors in oil-conductingheateabsorbing tubes with a minimum pressure drop.

In a great many methods of processing hydrocarbons (herein referred toas oil) and their derivatives, it is necessary to superheat the oilvapors. This is ordinarily done by passing the oil in liquid phase to avapor separator, where the pressure is reduced to produce as muchvaporization as possible. To maintain thepres sure as low as possiblewithin the separator, and thereby increase the percentage of oilvaporized, we connect the vapor outlet of the separator to a bank ofheat-absorbing tubes which, in accord with our invention, is soconstructed and arranged as to have an exceedingly low pressure drop,thus permitting a low pressure within the separator; lower thanheretofore possible, since less pressure differential is required toproduce forced ow of a given throughput through the tubes.

Though the pressure is low, the pressure differential is still such asto insure a suficiently high velocity within the tubes for good heatingconditions.

Further in accord with our invention, the cost of the pumping equipmentis greatly reduced for the same throughput, since `the pressure dropwithin the heating system is quite low.

In accord with a further aspect of our invention, the vapors aresuperheated while forced with a low pressure drop through a plurality ofvapor-conducting heat-absorbing tubes connected in parallel, withsubstantially equal elevation of temperature of the several vaporstreams.

In carrying out our invention in one form thereof, the oil in liquidphase is elevated in pressure, heated above its vaporizationtemperature, flashed, and the vapors then conducted to a heating systemwhere they are superheated. 'Io reduce the pressure drop and therebymaintain a low pressure within the separator, we provide one or morebanks of tubes with all of the tubes of each bank vconnected in parallelwith each other; specifically by means of headers whose cross-sectionalareas vary in accord with the volume of vapor passing therethrough. Morespecifically, from the inlet at one end of one header, thecross-sectional area decreases to the opposite end thereof, roughly inthe proportion of the decrease in tubes served by the header at anygiven point to the end opposite the said inlet. The opposite header oflike. cross-section is arranged so that its cross-section increases fromone end to the opposite end; the latter end forming the outlet from thebank of tubes. In this manner every vapor particle from inlet to outletof the bank traverses exactly the same distance as every other particle,regardless of the tube or path taken; and the parallel streams of vaporare elevated in temperature by substantially like amounts, since thevolume, or massvelocity of vapors through each tube is substantiallyequal to the mass-velocity through every other tube. Additionally, thetubes of each bank are preferably disposed in a row, adjacent the roofand floor of a heating chamber within which is projected intermediatethe banks, currents of hot combustion gases. The bank of tubes adjacentthe floor is disposed below and without the currents of hot gases, andeach of its tubes receives heat substantially solely by radiation withhigh and substantially uniform heat input to the tubes of that bank; andthe heat input or rate of heat transfer per unit area of heat-absorptionsurface per unit time as between the roof and licor-tube banks is or maybe of the same order of magnitude so that the heat inputs or rates asbetween the opposed banks are substantially the same.

For an illustration of one form of our invention, reference is to be hadto the accompanying drawings in which:

Fig. 1 is a combined vertical sectional view of heat-transfer apparatusembodying our invention, with diagrammatic representation of the mode ofits operation in a typical process;

Fig. 2 is a plan view, taken on the line 2 2 of Fig. 1 of oneheat-absorption structure;

Fig. 3 is an enlarged horizontal sectional elevation of one of theheaders of Fig. 1; and

Figs. 4, 5 and 6 are sectional elevations of the header of Fig. 3, andare respectively taken on the vlines 4, 5 and 6 of Fig. 3.

Referring to the drawings, we have shown our invention in one form asapplied to an oil-cracking system in which the charge oil, supplied tothe system by line IU, is elevated in pressure by a charge-pump Ii toinsure rapid now of the oil .through a bank of tubes I2 disposed in theconvection section C of a furnace or heater lll. After passage throughthe tubes l2, connected either in series or parallel, the oil, elevatedto desired vaporization temperature, is discharged by line l5 into avaporzing chamber I6. Before introduction into the vaporizing chamberI6, the pressure ofthe oil may be reduced Vby means of a lil) valve l1.In a manner well understood by the art, the oil in vaporizing chamber I6is separated into vaporous and liquid components. The liquid componentmay be withdrawn by line I8, under the control of valve I9, anddischarged from the system by line 20, or preferably used as reflux, orreturned to a heating coil for further elevation of temperature.

The vapors, still under substantial pressure and well above atmosphericpressure, are withdrawn from the chamber I6 by line 22 and introducedinto the inlet 23a of a header 23. As shown, the header 23, inconjunction with a second header 24, connects in parallel a plurality ofoil-conducting heat-absorbing tubes 25, ten of them being shown in thedrawings, though more or less than ten may be used.

After passage through the tubes 25, disposed horizontally adjacent theroof of fire chamber R, the vapors are discharged through the outlet 24hof the roof-tube bank, and by means of a connecting line 26 areintroduced into the inlet 21a of a header 21, which, in conjunction witha header 28, serves to connect in parallel a plurality, as ten,heat-absorbing tubes 29, all horizontally disposed adjacent the floor offire chamber R. The vapors are discharged from the floortube `bank 29 bymeans of outlet 28h, and by transfer line 30 they are conducted to otherapparatus for further processing, which apparatus is diagrammaticallyindicated at 3l. This additional apparatus is not illustrated in detail,since it may be of the conventional type well known to those skilled inthe art, and may include the usual devices, such as bubble towers andcondensers, for separating and liquefying products desired as motorfuel.

To generate heat, a plurality of muifles or combustion chambers 32 aredisposed horizontally alo-ng one wall of the re chamber R. Fuel of anysuitable character, preferably oil and/or gas, is introduced through theVenturi throat 33, together with the necessary air required forcombustion. The fuel is partially, or to substantial extent, burnedwithin the muffles 32. The hot, and burning gases, are discharged by themuffles 32 horizontally over and above the bank of floor tubes 29, whichare disposed below and without the current thereof for absorption ofheat substantially solely by radiation from the gases and refractory.

We prefer so to control the fuel pressure, the draft, and firingconditions, that the burning fuel issuing from the mufes passessubstantially entirely above and across the floor tube bank,convectively heating the exposed surface of bridge wall 35, beforetransfer of heat by convection to tubes i2. Some of the hot gases, dueto their tendency to rise, may to some extent convectively heat the rooftubes 25. The gases, after transfer of heat by convection to the tubesl2, are withdrawn to stack through the outlet passage 31.

In accord with our invention we reduce the pressure drop by subdividingthe oil in vapor phase, introduced at 23a, into a, plurality of streams,the ten streams shown being by way of illustration only, and not by wayof limitation. By so reducing the pressure drop Within theheatingsystem, a much lower pressure may be maintained within the vaporseparator I6 to produce a maximum vaporization of the oil in liquidphase therein. With said reduced pressure-drop and forced-now of vapors,we equalize the ow, the pressure drop, and the rise in temperaturebetween each of the subdivided streams by progressively decreasing thecross-sectional area of the header 23 from the inlet side, as the vaporstream is progressively subdivided by the parallel-connected tubes 25,and by progressively increasing the cross-sectional area of thereceiving header 24 to the outlet side, as the aforesaid subdividedstreams of tubes 25 are united within the header 24.

More specifically, and referring to Fig. 2, it is to be observed thetubes 29, interconnected by horizontally disposed headers 21 and 28, areof equal length. The cross-sectional area of the Vapor passage of header21 progressively decreases from its inlet end 21a to its opposite end21e, and the decrease is in proportion to the increase in the number oftubes receiving vapor as determined from right to left of the header asviewed in Fig. 2. Conversely, the cross-sectional area of the vaporpassage within the header 28 progressively increases from its inlet end28e to its outlet end 28h and in proportion to the increase in thenumber of tubes from right to left of header 28 as viewed in Fig. 2. Byarranging the inlet 21a diagonally opposite the outlet 28h inconjunction with the aforesaid features, the oil in vapor phase may beforced through the bank of tubes with a minimum pressure drop, with anoutlet pressure either above or below atmospheric pressure. Because ofthe number of tubes, the pressure drop between inlet and outlet isreduced to a minimum. By reducing the crosssectional areas of the vaporpassages, as described, we achieve a controlled flow of the vapors, andthere is forced through each of the tubes an equal quantity of vapor.

Not only are the tubes 29 of equal length, but the several passages frominlet 21a to oulet 281) are all equal. Taking two extreme cases, a vaporparticle may, from inlet 21a pass through the right-most tube 29 andthence through the full extent of the header 28 to its outlet 28h. Onthe other hand, a vapor particle may from inlet 21a traverse the fullextent of header 21 and from the left-most tube 29 pass to the outlet2819'. 'I'he paths traversed by the vapor particles in the two cases areexactly equal to each other, and the resistance to flow of vapor in thetwo cases is equal. Similarly, for any intermediate tube 29, the lengthof the passage from inlet 21al to outlet 28h is exactly equal to thelength of the passages of the two extreme cases just described; andequal to every other passage from inlet to outlet.

In accord with out invention, the pump Il, generally a costly piece ofequipment, may for the same throughput be of much smaller size than hasheretofore been the case, with a substantial saving, due to reductionsin first cost, in maintenance, and in operation. The amount of powernecessary to operate the pump l l is reduced because the system isoperated at a pressure materially lower than that required if the tubeswere serially connected. By reason of the equalized iiow between thetubes of each bank, there is no tendency for the iiow to becomeconcentrated within a few of the tubes, with concurrent reduction inquantity of vapor through the other tubes. If this were to occur, thetubes having the lesser amount of vapor would tend to overheat, withformation of coke or tarry deposits within the tubes. Also contributingto equalized flow is the arrangement of outlet and inlet of the headersat right angles to the tubes. This tends to diminish the effect upon thevapors of their velocity which would be in a direction `to cause unequaldivision kbetween the tubes.

As applied to processing systems in which the oil in vapor phase is tobe heated to high temperatures, but without substantial crackingof thevapors, it is particularly important that all of the vapors be equallyheated, and none to a temperature producing cracking thereof. We havefound that in .accord with our invention, this desired result may bereadily achieved, because equalized flow is maintained over wide changesin rates of flow, with the heat input or temperaturerise of the vaporstreams readily controlled in accord with the amount of fuel introducedinto the re chamber R by the muifles 32.

While each of the headers 23, 24, 21' and 28 may be circular incross-section, we have shown one of said headers, the header 28 in Fig.3, having a vapor passage which at the inlet end is, Fig. ci, circularin cross-section, and from the inlet end to its opposite end 28o, is inoval form gradually reduced in size as shown in Figs. 5 and 6. v

A further feature of our invention consists in the provision of closuresfor the clean-out openings opposite each of the tubes which conform tothe internal configuration of the header. The tubes are omitted in Fig.3. In the preferred construction, these tubes are inserted within theopenings 28d and are rolled against the header walls to form tight sealstherewith. Opposite each tube is a plug or closure 4G, shown ascircular, whose internal surface, the surface presented to the interiorof the header 28, forms a continuation of theinner wall of the header.In this manner,` the inner surface of header 28 is smooth throughout,and there are no projections or recesses to produce eddies, or othervariations in flow; nor is there any tendency for unequal division ofthe vapors between the plurality of tubes. Each closure 40 is providedwith a circular flange 4l, through which a series of cap screws 42 mayextend into an opposing cooperating flange of the header, tightly tosecure them in place. For simplicity, only the cap screws 42 for one ofthe closure members are shown. If desired, to reduce the weight of theclosure members, they may be provided with re-entrant openings 43.

While We have shown a particular embodimen.It of our invention, it willbe understood that we do not limit ourselves thereto, since many modiiications may be made, and we, therefore, contemplate by the appendedclaims, to cover any such modifications as fall within the spirit andscope of our invention.

What we claim is:

1. A system of superheating oil in vapor phase comprising a heatingchamber, means for producing a current of hot combustion gases withinsaid chamber, a plurality of oil-conducting heat-absorbing tubesdisposed adjacent the floor of said chamber below and Without thecurrent of said combustion gases, headers disposed horizontally andconnecting said tubes in parallel with each other, the internal area ofone header increasing from right to left across said bank and theinternal area of the other header increasing from left to right acrosssaid bank, and transfer lines connected to said headers where the areasthereof are maximum.

2. In a system of superheating oil in vapor phase, the combination of arow of tubes disposed in substantially the same plane, headers receivingthe opposite endsof said tubes for connecting them in parallel, theinternal area of one header increasing from right to left and theinternal area of the other increasing from left to right across said rowof tubes, each of said headers having clean-out openings opposite therespective ends of said tubes, and closures for said cleanout openings,each said closure having a portion which forms, with the internalsurface of said header, a smooth uninterrupted surface.

3. In a system of superheating oil in vapor phase, the combination of arow of tubes disposed in substantially the same plane, headers receivingthe opposite ends of said tubes for connecting them in parallel, theinternal area of one header increasing from right to left and theinternal area of the other increasing from left to right across said rowof tubes, said headers having walls including a flange forming aclean-out opening opposite each of said tubes, a closure for each'ofsaid openings including a flange cooperating with said flange of theWalls forming each of said openings,y each of said closures having aportion disposed within the said opening and of the same configurationas the inner surface of the header adjacent said opening.

4. 'Ihe method of superheating oil in vapor phase which comprisesforcing under elevated pressure a stream of oil in vapor phase from theinlet to theroutlet of a heating system, reducing the pressure dropbetween said inlet and said outlet by subdividing said stream into aplurality of streams, equalizing the flow and pressure drop between eachof said subdivided streams by passing said subdivided streams throughpaths, which paths, between said inlet and said outlet are of equallength, by progressively decreasing the cross-sectional area of thestream at the inlet side as that stream is progressively subdivided, andby progressively increasing the cross-sectiontional area of said streamat the outlet side as said subdivided streams are united.

5. A system of superheating oil in vapor phase comprising a pair ofheaders, a plurality of tubes in parallel with each other andinterconnecting said headers, one of said headers from its inlet endhaving a vapor passage whose cross-sectional area progressivelydecreases and the other of said headers havinga vapor passage whosecrosssectional area progressively increases to the outlet thereof,thereby to provide a plurality of passages of substantially equallength, as measured between said inlet and said outlet of said headers,means including a feed line connected to said inlet for producingforced-flow of said oil in vapor phase, and a discharge line connectedto said outlet and Within which are united the streams of oil in vaporphase flowing through said tubes.

6. A system of superheating oil in vapor phase comprising a heater,means for producing a current of hot combustion gases within saidheater, a bank of tubes within said heater, and so disposed With respectto said current of gases that the individual tubes thereof are equallyheated, a header, having an inlet at one end, connected to correspondingends of the tubes, the cross-sectional area of said header progressivelydecreasing from its inlet end to its opposite closed end, a secondheader, having an outlet at one end, connected to the opposite ends ofsaid tubes, the cross-sectional area of said second header increasingfrom its closed end to its outlet, and said second header so disposedwith respect to said first header that the closed end thereof isopposite the largest cross-sectional area of the other header, and meansfor. producing flow under elevated pressure of said oil in vapor phasefrom said inlet of one to said outlet of the other of said headers.

'7. A system of superheating oil in vapor phase comprising a heater,means for producing a current of hot combustion gases Within saidheater, a bank of tubes within said heater, and so disposed With respectto said current of gases that the individual tubes thereof are equallyrheated, a header, having an inlet at one end, connected to correspondingends of the tubes, the cross-sectional area of said header progressivelydecreasing from its inlet end to its opposite closed end inversely asthe sum of the cross-sectional areas of the tubes increases from theinlet to closed end of the header, a second header, having an outlet atone end, connected to the opposite ends of said tubes, thecross-sectional area of said second header increasing from its closedend to its outlet, and said second header sol disposed with respect tosaid first header that the closed end thereof is opposite the largestcross-sectional area of the other header, and means for producing owunder elevated pressure of said oil in vapor phase from said inlet tosaid outlet of said headers.

8. A system of superheating oil comprising a tubular heater including aheating chamber,

means for producing therein a current of hot combustion gases, a bank ofoil-conducting heatabsorbing tubes Within said chamber, an oilsupplyline, means for elevating the pressure of the oil in liquid phase andforcing the same at high velocity through said bank of tubes, Vaporizingmeans connected to said bank, a second bank of tubes adjacent the floorand a third bank of tubes adjacent the roof of said heater, the saidcurrent of hot gases passing between said second and third banks,headers for connecting the tubes of said second and third banks inparallel With each other, one header having an inlet for the tubes ofone bank and the other having an outlet for said tubes, each said headerprovided with said inlet having a vapor passage whose crosssectionalarea decreases in the direction of vapor flow, and the other of saidheaders associated with each bank having a Vapor passage whosecross-sectional area increases in the direction of vapor flow, means forconducting oil in vapor phase from said vaporizing means to the inlet ofone of said headers, means for connecting the associated outlet-headerto the inlet-header of the other bank of tubes, and a transfer lineconnected to the outlet-header of said other bank of tubes.

FRANK H. PRAEGER. THOMAS B. LEECH.

